Along with the technical evolvement and emerging data services, such a scenario may occur in later releases of the Long Term Evolution-Advance (LTE-A) system that a terminal is configured to operate while being served by a plurality of base stations (i.e., dual connectivity).
For example, a terminal is configured with a Master Evolved NodeB (MeNB) and at least one Secondary eNB (SeNB), where in the dual connectivity application scenario, at least an S1-MME (wherein MME stands for a Mobility Management Entity (MME), and S1 stands for an S1 interface to the MME) is terminated at the MeNB, so from the prospective of a core network, the MeNB can be regarded as a mobility anchor; and the SeNB is responsible for providing the terminal with an additional radio resource in addition to that provided by the MeNB.
In the dual connectivity scenario, frame structures applied to cells and/or carriers scheduled by different base stations may be the same, or may be different. For example, a Frequency Division Duplex (FDD) frame structure is applied over the respective carriers scheduled by the different base stations for the UE, or a Time Division Duplex (TDD) frame structure is applied over the respective carriers scheduled by the different base stations for the terminal (wherein TDD uplink/downlink configurations applied to the respective carriers scheduled by the different base stations may be the same, or may be different), or an FDD frame structure is applied over respective carriers in one frequency band, and a TDD frame structure is applied over respective carriers in another frequency band, for the terminal.
In the dual connectivity scenario, the plurality of base stations which the terminal is connected with schedule their respective sets of downlink carriers separately, where the method for scheduling and transmitting the data of terminal includes the following three options:
In a first option, bearers of the MeNB are routed directly to the MeNB from a gateway (e.g., a Serving Gateway (S-GW)); and bearers of the SeNB are routed directly to the SeNB from the gateway, that is, the bearers of the SeNB are not routed through the MeNB, as illustrated in FIG. 1;
In a second option, bearers of the MeNB are routed directly to the MeNB from a gateway; and bearers of the SeNB are firstly routed to the MeNB from the gateway, and then all the bearers are offloaded by the MeNB to the SeNB, that is, the bearers of the SeNB are not separated, as illustrated in FIG. 2; and
In a third option, bearers of the MeNB are routed directly to the MeNB from a gateway; and bearers of the SeNB are firstly routed to the MeNB from the gateway, and then a part of the bearers are offloaded by the MeNB to the SeNB, whereas another part of the bearers remain transmitted at the MeNB side, that is, the bearers of the SeNB are separated, as illustrated in FIG. 3.
In view of the complexity and cost of radio frequencies, the terminal may only transmit in a single cell/over a single carrier in the uplink; and since the terminal operating in the dual connectivity scenario above transmits over only one uplink carrier in the uplink, uplink control information generated by the terminal for the downlink carriers scheduled by the different base stations will be fed back to the respective base stations over the one uplink carrier, for example, Acknowledgement (ACK)/Negative Acknowledgement (NACK) feedback information for downlink data, from the base stations, received by the terminal will be fed back to the respective base stations over the one uplink carrier, and in another example, Channel State Information (CSI) generated by the UE for the downlink carriers scheduled by the different base stations will also be fed back to the respective base stations over the one uplink carrier.
However there has been absent so far a technical solution to transmission of uplink control information corresponding to downlink carriers scheduled respectively by a plurality of base stations in the dual connectivity scenario.